1. Field of the Invention
The present invention relates to a fuel hose used in a fuel piping within an engine room of automobiles. More specifically, the invention relates to a fuel hose in which an inner layer is formed of a fluororubber (FKM), an outer layer is formed of a blend (NBR.PVC) of an acrylonitrile-butadiene rubber (NBR) and polyvinyl chloride (PVC), and the inner and outer layers are adhered well by vulcanization.
2. Description of the Related Art
As such a fuel hose, a monolayered hose formed of an NBR.PVC blend with a weatherability is well known in which it is intended to improve a resistance to gasoline and an impermeability to gasoline with NBR and a resistance to ozone with PVC.
However, regarding the strict regulations to permeability to gasoline in recent years, only the monolayered hose is insufficient. The use of FKM which is excellent in the resistance to gasoline or the impermeability to gasoline has been also proposed, but FKM is costly.
Accordingly, an FKM/NBR.PVC fuel hose in which FKM is used in an inner layer and NBR.PVC that is less costly and is good in the resistance to gasoline, the impermeability to gasoline and the resistance to ozone is used in an outer layer is considered to be optimal. In this case, however, it is required that the inner and outer layers are adhered through simple adhesion by vulcanization so strongly as to satisfactorily prevent peeling-off therebetween. Thus, the method of adhesion by vulcanization becomes a problem.
JP-B-60-33663 describes a technique in which, when an inner layer is formed of FKM and an outer layer of an epichlorohydrin (ECO) rubber, the adhesion by vulcanization is enhanced by incorporating a carboxylic acid 1,8-diazabicyclo-(5,4,0)-undecene-7 salt (carboxylic acid DBU salt). JP-B-60-33662 describes that for adhesion between FKM and NBR a carboxylic acid DBU salt is incorporated in FKM or NBR and a basic silica-type filler and an epoxy compound are incorporated in NBR. However, JP-B-60-33663 only describes an adhesion recipe of FKM and ECO, and JP-B-60-33662 an adhesion recipe of FKM and NBR. A desirable recipe of adhesion by vulcanization of FKM and NBR.PVC is not suggested therein.
In JP-A-10-54485, an FKM/NBR.PVC fuel hose is briefly indicated in the description of the prior art, but the adhesion between the inner and outer layers and the recipe of adhesion by vulcanization thereof are not disclosed at all.
JP-A-9-196247 describes that a carboxylic acid DBU salt is incorporated in NBR.PVC to improve the adhesion with a material to be adhered. However, the material to be adhered is not FKM but a fluororesin. Besides, after vulcanization of NBR.PVC, a fluororesin is melt-adhered. Thus, it does not teach the adhesion by vulcanization between FKM and NBR.PVC.
JP-A-7-229584 is an invention concerning adjustment of a thickness ratio of inner and outer layers of an FKM/NBR.PVC fuel hose. With respect to the recipe of adhesion by vulcanization, it is described that a carboxylic acid DBU salt is added and a polyol vulcanizing agent is employed. However, owing to special circumstances that FKM is inherently poor in the adhesion with other rubber materials and it is all the more difficult to secure an adhesion strength with FKM by adding PVC for imparting a resistance to ozone to NBR, only the recipe of adhesion by vulcanization is not necessarily satisfactory to realize the good adhesion by vulcanization between FKM and NBR.PVC.
It is an object of the invention that a desirable recipe of adhesion by vulcanization between FKM and NBR.PVC is specifically worked out and thereby a fuel hose is realized in which FKM as an inner layer is firmly adhered to an NBR.PVC blend as an outer layer.
The object of the invention is achieved by a fuel hose (FKM/NBR.PVC) comprising an inner layer formed of a fluororubber (FKM) and an outer layer formed of a blend (NBR.PVC) of an acrylonitrile-butadiene rubber (NBR) and polyvinyl chloride (PVC) and adhered to the inner layer by vulcanization, wherein polyvinyl chloride having an average polymerization degree of from 700 to 1,750 amounts to from 15 to 45 parts by weight per 100 parts by weight of the blend, a carboxylic acid 1,8-diazabicyclo-(5,4,0)-undecene-7 salt (carboxylic acid DBU salt) represented by formula (1) 
, wherein R denotes a saturated or unsaturated hydrocarbon radical having a chain structure and/or a cyclic structure, or a derivative thereof, and the structure may contain atoms other than carbon atoms and hydrogen atoms, is incorporated in the blend, and a polyol vulcanizing agent is incorporated in the fluororubber.
In the invention having this construction, since PVC having the average polymerization degree of from 700 to 1,750 is used in the NBR.PVC blend, the vulcanizing adhesion with FKM is good. Since the lower limit of PVC in the blend is 15 parts by weight per 100 parts by weight of the blend, the resistance to ozone of the outer layer in the fuel hose is secured. Further, since the upper limit of PVC is 45 parts by weight, the adhesion strength of the blend to FKM is also good.
Further, since the carboxylic acid DBU salt is incorporated in the blend, the blend and FKM are firmly adhered by vulcanization. Still further, since the polyol vulcanizing agent is incorporated in FKM, the adhesion between the blend and FKM is all the more improved.
In the invention, the fuel hose is obtained in which these effects are exhibited synergistically, so that a satisfactory resistance to gasoline or impermeability to gasoline and the resistance to ozone are consistent and the inner and outer layers are hardly peeled off owing to the good vulcanizing adhesion between the FKM layer and the NBR.PVC layer.
The above and other objects, features and advantages of the invention will become more apparent from the following description.